Earth scientists gather geological information from rocks in order to understand the geological processes better. It is compulsory to examine rocks in detail for reliable geological deductions. Petrographical analyses, which inspect the rocks in terms of their physicochemical composition and texture, represent the primary step for accurate geological interpretations. Microscopy stands as the most frequently used tool for petrographical observations, although it requires destructive sample preparation. Pyroclastic rocks, which are formed by explosive volcanic eruptions, are usually friable and delicate by nature. These rocks tend to suffer from destructive sample preparation processes for microscopic investigations and usually lose initial textural characteristics during cutting, lapping, or polishing. X-ray microtomography is the state-of-the-art, 3D imaging method which uses X-rays passing through the sample to obtain spatial and structural information on componentry. Since X-ray microtomography is a nondestructive technique, it can be considered as an excellent complement for conventional petrographical methods, especially for fragile samples such as pyroclastic rocks. Once the rock components have been identified by preliminary petrographical studies, 3D quantitative information can be achieved from tomography datasets using image processing. This chapter presents the essential steps for microtomography studies and demonstrates quantitative modal componentry analyses on various pyroclastic rocks.